Marine Jet drives propelling a vessel based on water jet propulsion have long been known and used due to certain advantages over the traditional external ship's propeller. An engine driven impeller, rotating inside an impeller housing pumps water from below the vessel through an intake duct, then pressurizes and expels said water through a diffusor housing and a nozzle horizontally behind the vessel. A typical example of such a conventional marine jet drive is seen in U.S. Pat. No. 3,935,833, which shows a pump, that may be driven vertically or horizontally and is positioned near the bottom and transom of a marine vessel. The conventional jet propulsion systems have certain general advantages that make them especially attractive under circumstances where a conventional ship's propeller would be exposed to damage by contact with underwater objects. A jet drive has the further advantage that it does not produce appendage drag and is safe for swimmers and animals who could be hurt by the rotating blades of an external propeller.
The known jet drives have, however, certain drawbacks compared with the conventional external propeller propulsion system. A major drawback is caused by the lack of adaptability to specific engines and hull designs, because of the high expense of manufacturing a specific jet drive for each of a variety of applications.
Furthermore, the conventional jet drives rely in their design concepts on the predictability of the tensile, compression and shear strengths as well as the modulus of elasticity and coefficient of expansion, characteristic of certain metals, to maintain impeller alignment and clearance tolerances in relation to impeller housing, diffusor housing and intake duct. Because of the long unsupported span of the drive shaft in the intake duct, impeller tip clearance needs to be loose to allow for the flexing of said shaft and the relative movement of the forward bearing due to deformation under load of the conventional jet drive intake duct. This loose tip clearance detracts from jet drive efficiency. Operation in sandy water, using conventional jet drives is compounded by water lubricated impeller shaft bearing wear, that in turn causes impeller tip wear because of contact with the impeller housing, further loosening the tip clearance with a further detrimental effect on efficiency. The use of metals, as referenced above, in water produces corrosion and electrolysis, and its deleterious effects on efficiency and longevity of conventional jet drives have to be accepted.
The location of the engine in the vessel is compromised by the need for a flexible drive shaft in front of the conventional jet drive, requiring the placement of the engine further forward in the vessel, taking up more otherwise usable space. A further drawback is the difficulty in sealing a low pressure lubricating oil space from high pressure water generated by the impeller. Another drawback of conventional jet drives is caused by the inability of discharging the engine exhaust gas with the jet stream, leaving a significant heat, odor and noise signature, adversely affecting personnel on and near the vessel. Still another drawback is the large size and weight of the steering and reversing deflectors, used in conventional jet drives, as well as a lack of ability to steer the vessel in case of loss of engine power. Other drawbacks are that finding a neutral position by balancing forward and reverse thrusts, still causes slight vessel movement when no movement is wanted, requiring the presence of personnel at the steering station, to keep the vessel from changing position. Also, the fixed nozzle aperture and lack of trim control of a conventional jet drive allow for only one most efficient operating condition on marine vessels, that are characterized by a variety of loading and trim conditions.
Transom interference with forward water flow during reverse operation hinders the otherwise good reverse and maneuvering capability of a conventional marine jet drive; likewise, trim planes are incompatible in conjunction with conventional jet drive reversing systems because said planes block said forward water flow. Another drawback is the placement of steering and reversing hydraulic control cylinders, hydraulic hoses, position feedback cables, and lubricating hoses outside the vessel, exposed to water and the weather where corrosion and marine growth damage exposed rod ends, hydraulic seals and hoses.
Further, because of the recited deficiencies, conventional jet drives require time consuming disassembly and frequent servicing and repair.
There further is a tendency of waterborne debris to be caught in the water intake duct grid and the impeller or wrapped around the drive shaft of a conventional jet drive, with no quick means of removing it, immobilizing and endangering the vessel as the engine has to be tuned off to clear debris. Clearing the intake duct is a time consuming process, done through the access hatch from inside the vessel or by a diver from below the vessel. Some conventional jet drives have grid cleaning devices built in, however these devices are not effective, and give a false sense of security, and, they do not free the shaft or the impeller from debris.
It is accordingly a primary object of the present invention to provide a marine jet drive propulsion system that overcomes the disadvantages of the known jet drives. In particular, the jet drive according to the present invention provides better efficiency by having better matching capability to engine and hull design without high cost, by means of an exchangeable insert in the impeller housing, with matching impeller, altering the pump characteristics to best advantage of a particular application without changing the impeller housing. Similarly, the nozzle aperture can be changed without changing the nozzle housing by the use of fixed or controllable inserts.
Furthermore, the impeller is rigidly but rotatively supported inside the impeller housing, without the need of a stiff shaft and a bearing forward of the intake duct to maintain impeller alignment. Instead, an internal flexible drive shaft in the intake duct, connects the impeller with the engine, obviating an external flexible drive shaft. Thus, tighter impeller clearance, and better efficiency can be obtained. Any deformation of the intake duct under load, altering the position of the impeller housing and the diffusor housing and impeller shaft alignment in relation to the engine, will be absorbed by the flexible drive shaft. The engine may be placed on resilient mounts, as the output shaft movement in relation to the impeller shaft, likewise will be absorbed by the flexible drive shaft. The design concept using a flexible drive shaft eliminates the detrimental effect of a lower tensile, compression and shear strength, and the less predictable modulus of elasticity and coefficient of expansion of composite materials. The use of non-metallic, non-conductive materials avoids corrosion and electrolysis. The internal flexible drive line allows the engine to be placed further rearward to gain usable space in the vessel. The intake duct is provided with a shaft sleeve enclosing the flexible drive shaft, keeping water from coming into contact with said shaft. Material of construction of said drive shaft may be chosen entirely based on strength, without concern of corrosion and may be smaller in diameter and lighter in weight. The use of low cost, easily serviceable water and oil shaft seal arrangements is possible because of the tight tolerance of the impeller shaft bearings. A void space is provided between oil seal and water seal, connected via a port internal to diffusor housing and impeller housing to the vessel's interior, where a sensor may determine the presence of lubricant or water, alerting the operator to a seal failure. Similarly, lubricant feed and drain ports connect the bearing space inside the diffusor housing internally, then internal to the impeller housing to a reservoir inside the vessel. Said void space drain port and lubricant ports are produced as an integral part of the diffusor housing and impeller housing and avoid the need for external hoses exposed to the elements.
Furthermore, an engine exhaust internal to the jet nozzle is provided, to improve engine efficiency, because of suction created by the jet stream and improve personnel comfort by ejecting exhaust heat, noise and fumes with the jet stream. U.S. Pat. No. 3,943,876 shows engine exhaust in combination with the jet stream, however the exhaust is peripheral to the jet stream and is added behind the jet nozzle and is not internal to it and does not enhance efficiency or remove exhaust heat and fumes with the jet stream, nor does it suppress exhaust noise. U.S. Pat. No. 4,552,537 uses exhaust gases and engine generated heat to decrease behind-the-jet nozzle frictional losses between a submerged jet stream and surrounding water to render said jet stream more effective.
Further, the invention provides a combined steering and reversing mechanism that is lighter in weight and smaller in dimension and has improved performance. U.S. Pat. No. 4,538,997 displays a reversing means, whereby a single, centrally located reversing scoop moves up from the bottom of a steering tube, deflecting water for reversing down and forward. The present invention uses a single fixed split duct with right and left ports or twin reverse ducts, fastened to left and right steering deflectors, sending water flow forward and angled away from the intake duct during reverse operation and is in concept different from the referenced patent.
A discharge nozzle aperture control means is provided to allow most efficient performance at varying vessel conditions. U.S. Pat. No. 4,176,616 shows an externally applied two position thrust controller. The present invention in contrast does not control thrust, but refers to an internally attached permanent or adjustable nozzle aperture and directional trim control, that has as purpose the adaptation of the aperture of the nozzle to obtain most efficient operation under varying vessel conditions such as longitudinal center of gravity and vessel weight.
A set of steering vanes may be provided, attached to the outer surfaces of the reverse ducts, as they are fastened to the steering/reverse deflectors and move with said deflectors. U.S. Pat. No. 3,982,494 provides for an auxiliary rudder that is actuated by the jet pump pressure and swings out of the way at higher speeds, to reduce drag. The present invention uses the reverse ducts, also a subject of the present invention, to rigidly support the steering vanes.
Also provided is reverse operation eliminating backwash against the transom using a reverse/trim plane in close proximity to the jet drive, that retracts to a position above the reverse ducts during reverse operation forcing all forward water flow underneath the vessel. In forward direction the reverse/trim plane may be adjusted like a trim plane.
The mechanical or hydraulic controls, operating the combined steering/reversing deflectors, the nozzle aperture inserts and reverse/trim plane are placed inside the vessel to avoid marine growth and weather exposure. They are however attached to the impeller housing forward flange. Sliding control rods with water seals at the transom connect said deflectors, aperture inserts and reverse/trim plane to the mechanisms inside. This allows the installation and adjustment of said mechanisms to be done at the factory, without the need of having the intake duct present. Additionally, these control mechanisms have a park position whereby all control rods are pulled into their retracted positions, preventing damage from corrosion and marine growth to the sealing surfaces, while the vessel is idle for extended periods of time. Even in the event of failure of said water seals, only water will leak into the vessel and no oil will leak into the water, avoiding pollution and hydraulic system failure.
Further, there is provided an automatic zero movement neutral position by means of a centrifugal clutch that disengages at idle speed. An interlock is provided to prevent the clutch from engaging in the park position, to allow high idle speeds and starting of the engine without activating the jet drive.
Furthermore, a more efficient intake duct is provided by means of a gradually rising rearward edge of the bottom intake opening, forming a wedge shaped section back down to said intake opening. said rising rearward edge produces a diminishing apparent intake opening as the vessel moves faster in forward direction, while the wedge lower surface produces added lift to the vessel. U.S. Pat. No. 3,993,015 shows an elevated intake opening rearward edge parallel to the intake opening level, to permit a simpler manufacturing procedure and does not compare in relation to its position or its function. The invention further provides better protection of the intake duct against floating debris, by means of tapered grid bars as well as an intake debris removal system using pressurized fluid ejection from the grid bars, in a continuous manner or in a short burst. A debris cutting device is placed just forward of the impeller to prevent debris from wrapping around the impeller hub.
Further, construction, operation, weight reduction and maintenance features are part of the invention, as will be described in detail in the following presentation with appended drawings and claims.